System for generating discrete side-byside displays on a cathode ray tube



Oct. 7, 1958 Filed June 26, 1950 SYSTEM FOR GENERATING DISCRETESIDE-BY-SIDE W. G. ALEXANDER EI'AL DISPLAYS'ON A CATHODE RAY TUBE 6Sheets-Sheet 1 INVENTOR.

WILLIAM G. ALEXANDER CHARLES MCL. HARDEN 1958 w. G. ALEXANDER ETAL2,855,591

SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE DISPLAYS ON A CATHODE RAYTUBE Filed June 26. 1950 6 Sheets-Sheet 3 mu 4 Qh 386 Can 1 0x 33 025..555 2.

INVENTOR. WILLIAM G. ALEXANDER CHARLES MCL. HARDEN BY Jll Oct. 7, 1958we. ALEXANDER ETAL SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE DISPLAYSon A CATHODE RAY TUBE 6 Sheets-Sheet 4 Filed June 26. 1950 omT rohzsmmokou ww O ZOFPOMJM mm J l l I OmT R m w W.

WILLIAM G. ALEXANDER BY CHARLES MCL. HAR

w. G. ALEXANDER ETAL 2,855,591 SYSTEM FOR GENERATING DISCRETESIDE-BY-SIDE DISPLAYS ON A CATHODE RAY TUBE 6 Sheets-Sheet 5 Filed June26. 1950 INVENTOR. WILLIAM G. ALEXANDER YCHARLES MCL. HARDEN Oct. 7,1958 w. G. ALEXANDER ET AL SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDEDISPLAYS ON A CATHODE RAY TUBE Filed June 26, 1950 6 Sheets-Sheet 6United States Patent SYSTEM FOR GENERATING DISCRETE SIDE-BY- SlDEDISPLAYS ON A CATHODE RAY TUBE William G. Alexander, Baltimore, andCharles McL. Harden, Towson, Md., assignors to Bendix AviationCorporation, Towson, Md., a corporation of Delaware Application June 26,1950, Serial No. 170,326

3 Claims. (Cl. 54s 11 This invention relates to indicator systems andmore particularly to a system for providing, on the face of a singlecathode ray tube, a pair of simultaneous radar presentations eachdepicting the position of a common target with respect to referenceindicia, when scanned in a respective plane.

The invention has particular reference to Ground Controlled Approach orGCA systems in which an aircraft is guided to a landing under conditionsof poor visibility. In such systems as conventionally used, one or apair of radio pulse echo systems (radars) scan a region of spaceincluding the desired glide path. Two antennas are used, one scanningthrough a horizontal plane and the other scanning through a verticalplane. The antennas are oriented to pick up the target aircraft and thepilot is directed by radio communication to correct his flight path tobring it into coincidence with the desired glide path.

It has been customary, in the past, to present the indication from eachscan on a separate CR tube, calling one the elevation presentation andthe other the azimuth presentation. The fact that each presentation wason a separate tube made it necessary that a separate observer besupplied for each presentation. This added to the expense of operatingthe system.

The presentations, as normally used, are sectors of a plan positionindication which have been distorted for more advantageous use. In theirusual form they could not be combined on a single cathode ray tube facewithout overlapping unless they were reduced in size to an undesirableextent.

It is an object of this invention to provide a system by which a pair ofradar presentations can be simultaneously shown on the screen of asingle cathode ray tube.

It is another object of the invention to provide a system by which apair of radar presentations of a combined size greater than that of thecathode ray screen can simultaneously be shown on the said screenwithout a substantial reduction of size.

It is a further object of the invention to provide a system by which apair of radar presentations may be combined on a single cathode rayscreen in such positions that they would normally overlap, byeliminating the overlapping portions of the presentations.

It is a still further object of the invention to simultaneously display,on a single cathode ray tube screen, a pair of sectorial plan positionindications of such size that they would normally overlap and to inhibitthe generation of those portions which would normally overlap.

The objects and advantages of the invention are reali-zed by a system inwhich each plan position indication is developed in alternation with theother. The alterna- Referring now to the drawings:

Fig. 1 is a plan view of the screen ofa cathode ray tube bearing a GCAelevation presentation;

Fig. 2 is a similar view of azimuth presentation; n

Fig. 3 is a similar view ofa screen carrying both the presentations ofFigs. 1 and 2, with portions in a region of overlap curtailed;

Fig. 4 is a schematic block bodying the invention;

Fig. 5 is a schematic block diagram of a portion of the circuit of Fig.4;

Fig. 6 is a group of time related waveforms occurring in the circuitofFig. 5; v

Fig. 7 is a schematic diagram of the circuit of Fig. 5;

Fig. 8 is a schematic circuit diagram of an angle data selector circuitforming part of the circuit of Fig. 4; and,

Fig. 9 is a schematic circuit diagram of a circuit for clipping theazimuthand elevation presentations to prevent overlap, this circuitlikewise being a part of the circuit of Fig. 4. p

Referring now more particularly to the drawing, Fig.

diagram of a circuit em- 1 illustrates the circular screen 10 of acathode ray tube on which is displayed a distorted sector of a planposition indication generated by the elevation scanning antenna of a GCAinstallation. Displayed on the. surface of the screen, by some meansother than the cathode ray beam of the tube, is the outline of thepattern to which the indication generated by the tube is made toconform. This pattern may be permanently marked on the screen or maybeprojected on the screen from a source of visible or invisible light ormay be developed in any of a number of known ways. It consists of agenerally triangular outline 11 conforming to the shape of a distortedsector of a plan position indication, having its point of origin 12 atthe left hand side of the screen. A horizontal line 13 is also formedonthe screen to represent the ground level to which the glide path isreferred. The desired glide path is indicated by a line 14 which joinsthe ground line 13.,near the point of origin 12, the point of juncturerepresenting the point of desired touch down of an aircraft on therunway. Formed parallel to the glide path line 14 are a pair of dottedlines 15 which represent-reference distances from the glide path bywhich the error in elevation of a plane being guided can be visuallydetermined. Such lines could, for example, indicated distances of 50feet above and below the glide path.

Shown also in this figure are spaced vertical lines 16 resentative ofthe scan of the azimuth scanning antenna of the GCA system. The sectorhas its origin'at the point 18 located at the top of the screen and hasa triangular outline 19, having a horizontal base at the bottom of thisscreen. Erected on the base is a vertical line Zllrepresentative ofaplanview of the desired glide path as seen by a pilot of an approachingaircraft. A small rec-.

tangular representation 21 of the runway is formed at the top of theline 20. A pair of dotted lines 22 equally spaced on opposite sides ofthe line 20provide reference tion may occur at the end of each line ofthe scan or at the end of each scan. Portions of the two indicationswhich would overlap are electronically inhibited by the use of gateswhich are varied in duration as the scan developes.

indications of azimuthal discrepancies between the position of the planeand the glide path. These lines can,'for

example, indicate distances of 50feet on either side of v the glidepath. Horizontally extending range marks 23', are also formed on thisindication, either electronically a screen carrying a GCA vide a morerealistic indication to the observer.

by means of the cathode ray means or by the same means as the remainderof the indication.

On each of the displays of Figs. 1 and 2 the location of the aircraft isindicated by. a luminous dot generated electronically by the cathode raybeam of the tube in response to the video signal of the radar set orsets used in the system.

GCA systems as known to the art may employ either one or two radar setsin connection with the scanning antennas. If one radar set is used, theset is connected alternatively to each of the two antennas. Thealternation may occur at the end of each scan or at the end of each lineof the scan. If two radar sets are employed each set may be continuouslyconnected to a respective one of the two antennas. In order to eliminatecross talk when the latter type of system is used, the antennas may bepulsed in alternation only oneradar set being activated at a time. i

The present invention is concerned with a means by which the twodisplays of Figs. 1 and 2 may be combined on a single tube forobservation by a single observer without overlapping of the displays andwithout reduction of their size to a point at which their legibility 'isimpaired. This invention is useable for GCA systems employing either oneor two radar sets and in which the antennas are activated sequentiallyeither at the termination at the end of each line or of a termination ofan entire scan. A combined display in accordance with the invention isillustrated in Fig. 3. The screen of the tube is indicated at 26. Theelevation display similar to that of Fig. 1 appears in the upper half ofthe screen while the azimuth display similar to that of Fig. 2, butreoriented so that the glide path now lies in a horizontal direction, isformed on the lower half of the tube. The outlines 11 and 19 may bepatterns formed by means other than the cathode ray beam of the tube towhich the indications generated by the cathode ray tube are caused toconform just as in the displays of Figs. 1 and 2. It will be noted thatthe lower portion of the elevation display beneath the horizontal groundline 13 has been removed except for a small portion 11 at the left handedge of the display. It will also be noted that the upper portion of theazimuth display has been removed, the display now terminating in itsupper portion in a horizontal line 27 which runs parallel to the groundline 13 of the elevation display.

With respect to all three figures, it will be understood that theindication generated by the cathode ray beam of the tube is that of theusual sectorial plan position indication distorted in a manner known tothe art to pro- Thus, in each indication the cathode ray beam at thebeginning of each scan line starts at the point of origin of the displaysuch as point 12 in Fig. 1 and point 18 in Fig. 2 and proceeds radiallyfrom that point for a predetermined length of time and then flies backto that point and begins the generation of a second radial linedisplaced from the first by a small angular amount. This actioncontinues until the entire triangular indication has been generatedwhereupon the generation of the indication is repeated. If during thegeneration of the indication an aircraft is encountered by the radiatedbeam, the cathode ray beam of the tube is intensified to produce a spotof light on the indication representative of the position of theaircraft at that instant.

The same manner of generation is followed in Fig. 3, the two indicationsbeing generated by alternate excursions of the cathode ray beam. Thisalternation may occur either at the end of each line of each scan or atthe end of each complete scan as desired. In any event, the alternationoccurs so frequently that by reason of the persistence of vision of thehuman eye, the two scans do not appear in alternation, but rather appearas a constant unflickering presentation as though both weresimultaneously and continuously present on the tube screen.

There is shown in Fig. 4 a block diagram of an entire GCA systemembodying the invention. The system includes an azimuth scanning antenna30, the radiated beam of which has a cross sectional configuration asshown at 31 and scans in a horizontal path indicated by the line 32.Connected to this antenna, in the usual manner, for transmission andreception, is a radar transmitter and receiver 33. having a video outputterminal indicated at Z.

An elevation antenna is indicated at 34, the radiated beam of which hasa cross sectional configuration as indicated at 35 and scans in avertical path indicated by the line .36. To this antenna is connected,in the usual manner, for transmission and reception, a radio transmitterand receiver 37. The receiver of this set is provided with a videooutput terminal indicated at Y.

Both the scan paths 32 and 36 include the glide path down which incomingaircraft are to be guided to a landing. V

A cathode ray tube 38 having a screen 26 is provided upon whichthedisplay of Fig. 3 is to be presented. The cathode ray tube is providedwith horizontal deflection coils 39, 40 and vertical deflection coils41, 42 which operate in the usual manner. The tube is also provided witha cathode 43 and a pair of control grids 44 and 45. A horizontal drivercircuit 46 is provided which generates a current output having asaw-tooth wave form for defleeting the beam of the tube across thescreen in a horizontal direction in a known manner. A clamp circuit 24insures that the horizontal deflection voltage return to the samestarting value after each sweep. The vertical driver circuit 47 performsthe same function as circuit 46 with respect to vertical deflections ofthe cathode ray V. A clamp and cathode follower circuit 62 performsfunctions similar to circuit 24, as well as other functions which willbe described later. An intensifier circuit 49 is provided whichintensifies the cathode ray tube beam during each radial sweep to thepoint of producing a visible trace on the screen.

An azimuth video amplifier circuit 50 receives the video output of theradar set 33 by way of terminal Z and applies it to a video mixer 51.Here is is mixed with range marks generated in a manner to be laterdescribed and the output of the mixer is amplified in the video outputcircuit 52 and applied to the control grid 44 of the cathode ray tube.

An elevation video amplifier 53 receives the video output of radar set37 by way of terminal Y and after amplification applies it to the videomixer 51. The outputs of the amplifiers 50 and 53 are applied to thevideo mixer at different times as will be explained hereafter.

A range mark generating system is also supplied. This includes a rangemark delay circuit 51 triggered by pulses from, gate generator 60 bymeans of: which the point of origin, from which the range marks aregenerated, can be adjusted manually as desired. This circuit provides avariable delay means which operates ina known manner to perform thisfunction. The output of the circuit controls the phase of range markoscillations produced in a range mark oscillator and shaper circuit 52.This circuit contains an oscillator producing an output having afrequency selected to result in the generation of range marks separatedby desired intervals, the usual interval being a mile. The output ofthis oscillator is clipped into a square wave form and utilized tosynchronize a range mark blocking oscillator 53. A range mark startingcircuit 54 is provided which initiates the action of the blockingoscillator 53. The output of the range mark blocking oscillator 53 isapplied to the video mixer 51 with the result that the output of thismixer consists of video signals received from the radar set 33 or 37combined with range marks. 1

The portion of the circuit of Fig. 4 which has been de scribed above isof a conventional nature. The remainder of the circuit of this figurehas been added in accordance ans display of azimuth and elevationinformation on the screen 26. In order to accomplish this result, it isnecessary that the azimuth and elevation displays be generated inalternation. In order to generate such displays in alternation,switching arrangements must be provided so that, for example, when theelevation display is being applied to the screen, each line of the scanwill start from the point of origin which has been selected for thatdisplay and which is different from the point of origin selected for theazimuth display. There likewise must be utilized video informationcoming from the radar set 37 and angle data voltage related to theposition of the elevation antenna 34.

As has been stated, there are two possible methods of generating thedisplays, in the first of which the displays are generated inalternation after each scan line, thus one line of the scan of theelevation antenna will be generated and then a line of the scan of theazimuth in dication will be generated. The other alternative is togenerate the entire elevation scan and then generate the entire azimuthscan. In this description it will be considered that the alternationoccurs after each line of the scan.

Thus, following the generation of one line of the elevation scanutilizing the elevation video information and angle data voltage, it isnecessary that the system now be switched to receive only data from theradar set 33 and the azimuth antenna 30. This switching between azimuthand elevation data must occur at the pulse repetition frequency utilizedby the radar sets. For purposes of illustration, we may assume that thisfrequency is 2400 cycles per second.

The system as shown in Fig. 4 includes an electronic selector switch 55which performs several of the switching functions referred to above.This switch is triggered by a system trigger generated elsewhere in thesystem and recurring 2.400 times per second. The switch generatestriggers which are applied by conductors 56 and 57 to the transmitter ofthe azimuth radar set 33 and the transmitter of the elevation radar set37 respectively. these triggers are separated by time intervals ofapproximately 215 micro-seconds. These triggers are also supplied byconductors 58 and 59 to a gate generator 60 which generates a series ofsquare gating pulses that are applied to various parts of the circuit ina manner to be described later.

The selector switch 55 also performs the function of alternatelyswitching the video input to the cathode ray tube from that supplied byradar set 33 to that supplied by radar set 37 and back again. In orderto perform this function the selector switch generates gates which occurin alternation and each of which is supplied to a respective one of thevideo amplifiers 50 and 53 so that these amplifiers are gated into aconductive state in alternation.

In connection with the azimuth and elevation scanning antennas there areproduced a pair of voltages which vary as a function of theinstantaneous scanning position of the respective energy beams emittedfrom these antennas. These antennas may each comprise a linear array ofdipoles mounted on a variable width wave guide as described in volume26, entitled Radar Scanners and Radomes of the Radiation LaboratorySeries, published 1948 by McGraw-Hill Book Company, Inc, New York City.The description will be found on pages 185-193 inclusive. The width ofthese antennas is cyclically and synchronously varied to produce thescanning of their beams. This width varying means may, by a simplemechanical linkage, be caused to vary the setting of a pair ofpotentiometers to produce the pair of voltages referred to. Thesevoltages are used to modify the vertical deflection current applied tothe coils 41 and 42 in order that distortion of the display may besecured in order to produce the presentations in the manner illustrated.These voltages are also employed to clip the presentations throughtheuse of. gating voltages in order that the two dia- "6 plays maybeapplied to the same cathode ray screen in the manner illustrated inFig. 3. In order to carry out these functions the electronic selectorswitch 55 produces a pair of gating voltages which are applied to anangle data selector 61, the output of which is applied to the clamp andcathode follower circuit 62. The angle data selector receives inputvoltage from the antennas .30 and 34 by way of conductors 63 and 64. Thegates developed by the switch 55 determine which of these input voltagesis to be utilized at a given time since they also are employed inalternation. A map clipper 65 is employed to generate the necessarygating voltages for clipping the azimuth and elevation displays asillustrated in Fig. 3. This circuit receives an input from the angledata selector 61 of the angle data passed by that circuit and alsoreceives gating voltages from selector switch 55.

In order to establish the respective points of origin of the azimuth andelevation displays, a pair of centering circuits are employed, eachestablishing one component of the points of origin of these displays.The centering circuit related to the horizontal deflection systemcomprises a triode 66, the anode of whichis connected by way of aresistor 67 to the coil 39 of the horizontal deflection system. Thecontrol electrode of this tube re ceives gating voltage from theselector switch 55 by way of a conductor 68. The centering systemrelating .to the vertical deflection system comprises a triode 70, theanode of which is connected by way of a resistor 71 to the coil 41 ofthe vertical deflection system. The control electrode of this tubereceives gating voltage from the selector switch 55 by way of aconductor 72.

The make-up and functioning of the electronic selector switch 55 is morefully set forth in Figs. 5, 6 and 7. Fig. 5 is a block diagram of theswitch, while Fig. 6 illustrates the wave forms at different points ofthe circuit of Fig. 5. The wave forms are identified by block letters Iin Fig. 6 and the points where they are found in Fig. 5 are likewiseindicated by the use of the same letters. The basic element of theswitch is a multivibrator circuit 73, having a 50% duty-cycle, thecomplete cycle occupying a time of approximately 430 miro-seconds. Thesystem trigger is applied to the input of this circuit from the terminalX. This trigger has a wave form such as shown at A in Fig. 6. It can beseen that this wave form comprises a series of positive impulsesseparated by time intervals of 430 micro-seconds. The output of themultivibrator 73 is taken at two points, differentiated and applied asthe wave forms B and C to the inputs of two isolation amplifiers 74 and75. Wave forms B and C are seen to be the differentiated products of theoutput of a multivibrator having a 50% duty-cycle. Each wave formconsists of a series of impulses of alternate polarity, mpulses ofpositive polarity being produced at the leadmg edge of the positiveportion of the multivibrator wave form and impulses of negative polaritybeing produced at the leading edges of the negative portions of themultivibrator wave form. The impulses of the two wave forms are reversedin polarity. The isolation amplifiers 74 and 75 eliminate the negativegoing impulses and amplify the positive going impulses of these waveforms to produce output wave forms D and E. These two wave forms areapplied as triggering voltages to the transmitters of radar sets 33 and3'7 and to the gate generator 60 as described above in connection withFig. 4. These wave forms are also utilized as triggering voltages in twomicro-second multivizrators 76 and 77. The outputs of thesemultivibrators are the wave forms F and G which are seen to be squarepulses of 80 micro-seconds duration, separated by time'intervals of 430micro-seconds. The pulses of each of these wave forms occur midway ofthe pulse intervals of the other.

. One of the two multivibrators 76 and 77 maybe identically duplicatedin the gate generator 60, since the output of that generator is a waveform identical with the sum of F and G. If desired, the mutlivibrators76 and 77 may be utilized as the gate generator 60 with appropriateoutput leads to the various elements of Fig. 4 which are shown asreceiving the 80 micro'second pulse output of generator 60. For clarity,however, a separate gate generator 60 has been illustrated in Fig. 4.The outputs of the multivibrators '76 and 77 are applied to respectiveisolation amplifiers 78 and 79. The output of these amplifiers isapplied to the map clipper circuit 65 which will be later described.

The output wave form F from multivibrator 76 is also diiferentiated toproduce the wave form H which is 'applied to the input of a 215micro-second multivibrator 80.

From this circuit two wave forms I and K are recovered,

these being taken from points of opposing polarity in the output circuitof the multivibrator. As will be seen, these wave forms consist ofsquare waves having alternating, positive and negative going portions of215 microseconds duration. The positive portions of these wave forms areutilized as gates for various parts of the circuit of Fig. 4. It will benoted that these positive portions occur in the two wave forms inalternation. They are amplified in gate amplifiers 81 and 82 before use.The wave forms J and K are applied to the angle data selector 61 inwhich circuit they are utilized in a manner to be later described. Thewave form J is also applied to the control electrodes of centering tubes66 and 70 which have been previously described. The application of thiswave form to these tubes causes the conduction thereof to be shiftedbetween two difierent levels, one level occurring during the applicationof data relating to the elevation presentation to the cathode ray tubeand the other level occurring during the presentation of data relatingto the azimuth presentation.

Turning now to Fig. 7, we find that the multivibrator 73 comprises thetwo tubes 85 and 86 and their associated circuit elements. The wave formA is applied from terminal X to the control electrode of tube 85 whichis normally in a non-conducting state. The positive impulses of thiswave form trigger the multivibrator by causing the tube 85 to conduct.Once this action has been started, the Wave form A synchronizes theaction of the multivibrator to its recurrence. The wave form 13 consistsof the impulses of wave form A plus negative going impulses derived fromthe control grid of tube 85. When this tube ceases to conduct at thechange-over point of the multivibrator action, the negative goingimpulses are derived by differentiation of the control electrode voltagein the network composed of condenser 87 and resistor 88. This wave formis applied to the control electrode of a tube 89 which is a part ofisolation amplifier 74. The wave form C is derived from the anode oftube 85 by differentiation of the leading edges of the excursions of themultivibrator output. This differentiation occurs through a networkcomposed of condenser 90 and resistor 91 and the resulting wave form isapplied to the control electrode of a tube 92. which, with its cincuitelements, comprises isolation amplifier 75.

The wave forms D and E are derived from the oathodes of tubes 89 and 92respectively, from whence they are applied to the transmitters of radarsets 33 and 37 and I to the input circuits of multivibrators 76 and 77.Multivibrator 76 is composed of tubes 93 and 94 and their associatedcircuit elements and multivibrator 77 is composed of tubes 95 and 96 andtheir associated elements. The wave form D is applied to the controlelectrode of tube 93 and the wave form E is applied to the controlelectrode of tube 95.

The wave form F is derived from the anode circuit of tube 94 ofmultivibrator 76 and the wave form G is derived from the anode circuitof the tube 95 of the multivibrator 77. The wave form F is applied tothe control electrode of tube 97 which, with its circuit elements,constitutes the isolation amplifier 78 and the wave form G is applied tothe control electrode of the tube 98 which is a part of the isolationamplifier 79. Outputs from the cathodes of these tubes are available asgating voltages and are utilized for this purpose in the map clippercircuit 65.

The wave form H is derived from a variable tapping point on a resistor99 in the anode circuit of tube 93. The voltage from this point isdifierentiated through a network consisting of condenser 100 andresistor 101, and is applied to the control electrode of a tube 102which, with a tube 103 and their associated circuit elements, comprisesmultivibrator 80. From the anode circuit of tube 102 is derived the Waveform K, while the wave form J is taken from the anode circuit of tube103. These wave forms are applied to the respective control electrodesof two tubes 104 and 105 which respectively, with their associatedcircuit elements, constitute gate amplifiers 81 and 82. From the cathodecircuits of these tubes the wave forms I and K are available and aresupplied to the necessary elements of the circuit of Fig. 4.

The schematic circuit diagram of the angle data selector 61 isillustrated in Fig. 8. In that figure we find a pair of terminals 106and 107 across which azimuth angle voltage from the azimuth scanningantenna 30 is applied to the anodes of a pair of clamping tubes 108 and109 through a pair of resistors 110 and 111. Voltage ofthe Wave form Kis applied from terminal 112 to the control electrodes of these tubes.Across a second pair of terminals 113 and 114 elevation angle voltagefrom elevation scanning antenna 34 is applied through resistors 115 and116 respectively, to the anodes of two clamp tubes 117 and 118. Voltageof the wave form J is applied tothe control electrodes of these tubesfrom terminal 119. The control grids of tubes 117 and 118 are connectedthrough a resistance network to a source of negative voltage representedby terminal 120. This source establishes a bias on these grids ofsufficient magnitude to render the tubes non-conductive in the absenceof a positive voltage applied to the control grids. On the other handthe tubes 108 and 109 are conducting in the absence of a negativevoltage applied to their control grids.

A pair of tubes 121 and 122 have their cathodes directly connected andconnected through a resistance network to the terminal 120. The controlelectrode of tube 121 is connected to the anode of tube 108 acrossresistor 110 and the control electrode of tube 122 is connected in thesame manner to the anode of tube 117 across resistor 116. An outputterminal 123 is directly connected to the cathodes of these tubes.

A pair of tubes 124 and 125 have their cathodes directly connected andconnected through a resistive network to the terminal 120. The controlelectrode of tube 124 is connected to the junction between the anode oftube 109 and resistor 111 and the control electrode of tube 125 isconnected to the junction of the anode of tube 118 and resistor 115. Aterminal 126 is directly connected to the cathodes of these tubes.

In the operation of this circuit the tube 108 is normally heavilyconducting. The application of the negative going excursion of the waveform K to its control grid is sufiicient, however, to cut-off conductiontherein. So long as tubes 108 and 109 are conducting, their anodevoltage, applied to the control grids of tubes 121 and 124, issufficienttorender these tubes non-conducting so that the application ofazimuth angle voltage to the terminals 106 and 107 is ineffective toproduce an output at the terminals 123 and 126. Due to the reversedpolarity of the wave forms I and K at the times when tubes 108 and 109are conducting and no azimuth angle voltage may, therefore, be derivedfrom terminals 123 and 126, a negative going excursion of the wave formJ is being applied to the control electrodes of tubes 117 and 118. This,in

conjunction with the application of biasing voltage from the terminal120, maintains these tubes in a non-conductive state so that elevationangle voltage being applied across terminals 113 and 114 is efiectivelyapplied to the control electrodes of tubes 122 and 125 causing thosetubes to conduct. Since the terminals 123 and 126 are directly connectedto the cathodes of tubes 122 and 125 elevation angle voltage isavailable across terminals 123 and 126.

Now as soon as a negative going excursion of the wave form K is appliedto the control grids of tubes 108 and 109, conduction in these tubes iscaused to cease, with the result that the tubes 121 and 124 are nowrendered conductive and azimuth angle voltage is therefore appliedacross the terminals 123 and 126. At the same time a positive goingexcursion of the wave form J is being applied to the control electrodesof tubes 117 and 118, with the result that these tubes are now renderedconductive and by their conduction render tubes 122 and 125nonconductive. During this period of time, therefore, no elevation anglevoltage is applied across terminals 123 and 126.

It can thus be seen that elevation angle voltage and azimuth anglevoltage are alternately available from the output of this circuit duringsuccessive periods of 215 micro-seconds each.

Fig. 9 shows a schematic diagram of the map clipper 65 and of the clampand cathode follower circuit 62 and the vertical driver circuit 47. Theclamp and cathode follower circuit comprises a cathode follower circuitutilizing a tube 127, the output of which is taken from its cathode andsupplied through a potentiometer 128 to the control electrode of tube13tl,'forming a part of the vertical driver circuit. Angle data voltagefrom the angle data selector 61 is supplied to the control electrode oftube 127 by way of a terminal 129. A clamp tube 155 has its anodeconnected to the control grid of the tube 130 and receives pulses fromthe gate generator 60 by way of terminal 156.

The tube 130 is connected for operation as a relaxation oscillator withan output which has a saw-tooth. wave form. To this end the anode isconnected to B-I- through an inductance 157 and a feedback path from theanode to the control grid is provided by way of a resistor 158 andcondenser 159. The output voltage of this circuit is the verticaldeflection voltage applied to the vertical deflection coils 41 and 42 ofthe cathode ray tube. It is also utilized in the map clipping circuit ina way-to be described.

The tube 130 can only be rendered conductive during the receipt of agating impulse from the gate generator 60 by way of clamp tube 155 andthe time constants of the circuit 47 are such that each saw-tooth of itsoutput occupies the whole duration of the gating impulse, the controlgrid of the tube 130 being returned by the clamp tube 155 to a fixedreference voltage at the end of each gating impulse. The angle datavoltage applied by the cathode follower 127 governs the amplitude of theoutput sawtooth of circuit 47.

The output of the circuit 47 is shown as a negative going saw-toothexcursion 131 which is applied by way of a condenser 132 to a resistor133. This resistor is connected as a potentiometer to the control gridof amplifier tube 134. The wave form of the voltage applied to this gridby way of the potentiometer is indicated at 135. The cathode of thistube is connected by way of a potentiometer 136 to a source of negativevoltage indicated by the terminal 137. This tube will conduct during theinitial portion of the wave form 135 depending upon the setting of thepotentiometer 133. The final portion of the wave form 135 will, however,cause the tube to be cut-off with the result that an output Wave form asindicated at 138 will be produced. This output will have the form of asubstantially square topped, positive going pulse. The duration of thispulse is seen to be dependent upon the amplitude of the negative goingsaw-tooth 131 which is governed by the angle data voltage. The terminaledge of the pulse 138 is fixed, so that an increase in the ampli- .tudeof the wave form 131 will result in the leading edge of the pulse beingadvanced in time and a decrease of wave form 131 amplitude will have theconverse efiect.

The pulse is ditferentiated in the network comprising a condenser 139and a resistor 140 to produce a resulting wave form of the type shown at141 which is applied to the control grid of a pentode coincidence tube142. This tube is normally in a non-conducting state due to theapplication of a negative voltage from a source in dicated by a terminal143 through the resistor 140 to the control gird. Thesuppressor grid oftube 142 is connected by a resistor 144 to ground. Negative voltage issupplied by way of a terminal 145 through a resistor 146 to the junctionof resistor 144 and the suppressor grid. Likewise applied at this pointis the wave form G which is applied from the selector switch 55 by wayof a terminal 147 through a resistor 148. The tube 142 is normallybiased so heavily that it requires the coincidental application of thepositive going spike of the wave form 141, and a positive goingexcursion of the wave form G to render it momentarily conducting. Whenthis occurs a negative going spike, as indicated at 149, will be appliedto the input circuit of a one shot multivibrator 150. This multivibratorcomprises a pair of tubes 151 and 152. The control grid of tube 151 isconnected to 13+ through a resistor 153 of such value that this tube isnormally conducting and tube 152 is normally nonconducting. Theapplication of the negative going spike 149 to the control grid of tube151 triggers the multivibrator through one cycle of its operationwhereupon it returns to its initial condition and remains in that stateuntil the receipt of another negative triggering spike. Output from themultivibrator is taken from the anode of tube 152 at terminal 154'and isapplied by way of conductor 48 to the electrode 45 of the cathode raytube 38, as shown in Fig. 4. It can be seen that this voltage in thenormal state of the multivibrator 150 will be a positive voltage. Uponthe application of the negative trigger 149, the multivibrator willgenerate a negative going voltage excursion which will have a durationdependent upon the time constants of the multivibrator circuit.

The portion of the map clipping circuit which has been described is thatwhich performs the function of clipping the azimuth presentation whichis the lower presentation of Fig. 3. It can be seen from that figurethat it is necessary to clip the upper portion of the presentation alonga horizontal line. This is accomplished through the effect of the angledata voltage, the gate impulses from gate generator 60, and the waveform G upon the circuit described above. The application of wave form Gto the suppressor grid of tube 142 insures that that tube can conductonly during those times when angle data voltage from the azimuth antennais available from the angle data selector 61. The angle data voltageapplied by way of terminal 129 and tube 127 regulates the amplitude ofthe saw-tooth wave form 131 in the manner described so that theamplitude of that wave form is a function of the instantaneous scanningposition of the energy beam from the azimuth antenna with the amplitudeof the wave form increasing as the antenna scans from left to right asviewed by an incoming pilot. Until the scan position has moved to apoint several degrees to the right of the horizontal base line of theazimuth scan, the amplitude of the wave form 131 is too small to causethe production of a pulse 138 in the output of the tube 134 and thus themultivibrator 150 is not triggered and no clipping occurs. As the scanposition reaches this point, however, the

amplitude of the wave form 131 has increased to an amount sufficient tobegin with a production of pulses 138 in the output of tube 134. Thusthe circuit begins to clip the upper portion of the presentation nearthe right hand edge of the cathode ray screen. As the beam swingsfurther to the right, the amplitude of the wave form 131 increases andthe leading edge of the pulse 138 11 occurs progressively earlier intime with the result that clipping now occurs sooner in the duration ofeach radial trace of the beam of the cathode ray tube. With propercontrol of the variation of the amplitude of the wave form 131, as theantenna beam swings to the right, the line 27 marking the upper boundaryof the azimuth scan may be made to be horizontal.

We come now to the portion of the map clipper which effects the clippingof the elevation presentation or the upper presentation of Fig. 3. Thisportion of the circuit includes a multivibrator 160 of the one shot typewhich, on being triggered, generates a positive pulse 161 ofapproximately micro-seconds duration and then reverts to its quiescentstate until it is again triggered. This multivibrator comprises a pairof tubes 162 and 163. System triggering voltage of negative polarityresembling the wave form A is applied to the control grid of tube 162 byway of terminal 164. Elevation gating voltage of the wave form F isapplied to the anodes of the multivibrator tubes through resistors 165and 166 respectively, by Way of terminal 167. An amplifier 168 isprovided having its anode connected to the anode of tube 162 and itscathode connected to ground by way of a variable tap on a resistor 169.Positive voltage from a source B-]- is applied to the cathode by way ofterminal 170 and resistor 171. Elevation angle data voltage is appliedto the control grid of tube 168 by way of the terminal 172. The anode oftube 162 is connected to a source of negative voltage through acondenser 173 and a resistor 174 by way of a terminal 175.

The multivibrator 160 is not operative in the absence of a positivegating voltage of wave form F. When this voltage is applied to theanodes of the multivibrator tubes, the multivibrator is in its quiescentstate. The application of the negative system trigger voltage to thecontrol grid of tube 162 would result in the triggering of themultivibrator if it were not for the presence of the tube 168. When theelevation antenna beam is in the above ground portion of its scan theelevation angle data voltage applied to the grid of tube 168 causes thattube to conduct sufiiciently to maintain the anode voltage of tube 162at a value such that the negative system trigger applied to its controlgrid cannot be amplified and the multivibrator fails to respond to thatstimulus. When, however, the elevation antenna scan moves to a positionbelow the ground level the elevation angle data voltage is reduced untilthe tube 168 nears the point of cut-off. In this condition the anodevoltage on tube 162 is high enough in the presence of the wave form F torespond to the system trigger and to generate its output pulse 161. Thispulse is applied through a variable tap on resistor 165 and by way of acondenser 176 to the control grid of tube 151 of multivibrator 150. Thetra'ilingedge of this pulse triggers the multivibrator 150 into itsunbalanced state. It can thus be seen that during the duration of thepositive going excursions of the wave form F the multivibrator 160 isactivated but unable to respond to the system trigger until the scanposition of the elevation antenna moves below ground. At this time themultivibrator responds to the system trigger to generate the pulse 161.This pulse is of sufficient duration to allow the generation of theportion 11 of the elevation presentation shown in the upper part ofFig.3. The trailing edge of this pulse initiates the output pulse of themultivibrator 150 which blanks the cathode ray tube for the duration ofthe sweep of each sweep of the cathode ray beam following thetermination of the pulse 161.

To summarize the operation of the entire system depicted in Fig. 4, wehave a pair of antennas scanning a common region containing a glide pathdown which aircraft are to be guided to a landing. The azimuth antenna30 has a directive beam 31 scanning along the horizontal path 32. Theelevation scanning 34 has a directive beam 35 scanning vertically alonga path 36. The azimuth and elevation antennas are connectedrespectively, to two radar sets 33 and 37.

An electronic selector switch is provided which responds to a systemtrigger, consisting of an impulse generated at regular intervals of 430micro-seconds, to generate various output impulses. t generates twotriggering voltages of the wave forms D and E corresponding in form tothe .wave form of the system trigger A but with the impulses of one waveform occurring midway of the intervals between the impulses of theother. These impulses are utilized to trigger the two radar setsalternately into activity, a single radar pulse being transmitted uponthe receipt of each trigger. The same triggering voltages are alsoapplied to a gate generator which generates an 80 micro-second positivegoing impulse upon the receipt of each trigger. These 80 micro-secondimpulses are utilized in several portions of the circuit. They activatea range mark generating circuit. They also activate horizontal andvertical drivers which generate deflection voltages for the deflectioncircuits of a cathode ray tube 38. They are also applied to anintensifier circuit which causes the generation in the cathode ray tubeof a beam of sufficient intensity to produce a visible trace on the tubescreen for the duration of the impulse.

The video output of the radar receivers of sets 33 and 37 are appliedrespectively to azimuth and elevation video amplifiers 50 and 53. Theseamplifiers are also activated in alternation by 215 micro-secondimpulses generated by the selector switch 55. This alternate activationrenders each amplifier active at a time when its respective radar set istransmitting a pulse and receiving video information from any targetswhich may be present. The output of these amplifiers is mixed with therange marks generated by the range mark generating circuit and appliedto the cathode ray tube. The wave form I is also applied to the controlgrids of two centering tubes 66 and 70 which operate on the twodeflection circuits and, by virtue of the alternating levels of the waveform J, cause the two displays on the tube screen to be generated atdifferent locations on the screen.

Angle data voltage is also generated by each of the antennas 30 and 34and used to control the clipping of the two presentations in order thatthey may be displayed on the screen in as large a size as possiblewithout overlapping at their adjacent edges. To perform this function anangle data selector 61 and a map clipper circuit 65 are provided. Theangle data selector is controlled by the two wave forms I and K andthereby caused to alternately present in its output angle data voltagefrom each of the two antennas. This alternation is in synchronism withthe activation of the two video amplifiers and the two centering tubes66 and 70, in order that everything pertaining to each respectivepresentation he segregated into respective alternating time intervals.The map clipper 65 receives voltages of the two wave forms F and G andthe elevation trigger voltage of wave form D from the selector switch55. It also receives angle data voltage from the angle data selector 61and has applied to it the output of the vertical driver 47. From theseinputs it generates gating voltages appropriate to each presentationduring the time intervals when that presentation is being generated andclips each respective presentation along the portion of its boundarywhich is adjacent to the other presentation and would otherwise overlap.

It should be understood that the values of voltages and times that havebeen given herein are for the purpose of illustration only and are notto be considered as restrictive of the invention.

What is claimed is:

1. In a system comprising a directive antenna provided with means tocause the beam thereof to scan in a repetitive pattern; a radio pulseecho system connected to said antenna to transmit energy pulses theretoand receive video signals therefrom; a cathode-ray tube; meansrepetitively deflecting the beam of said cathode-ray tube in synchronismwith the pulses radiated by said antenna in a manner to generate arepresentation of the area scanned 13 by said antenna and the locationof objects therein, said deflecting means comprising a relaxationoscillator triggered in synchronism with said pulses to generate asaw-tooth waveform, means responsive to said waveform to deflect the rayof said cathode-ray tube and having said waveform applied thereto, meansgenerating a voltage which is a function of the instantaneous scanposition of said antenna and means applying said generated voltage tosaid relaxation oscillator to vary the amplitude of said output waveformthereof; and means applying the video signal from said antenna tomodulate the intensity of the beam of said cathode-ray tube: thecombination therewith of means for clipping a portion of saidindication, said clipping means comprising normally quiescent meansoperating when excited to generate a blanking impulse having a durationat least as great as that of one radial sweep of said beam in thegeneration of said pattern, means applying said impulses to saidcathode-ray tube in a manner to inhibit excitation of the screen thereoffor the duration of said impulses and means exciting said blankingpulses generating means, said exciting means comprising means responsiveto said output waveform and having aid output waveform applied thereto,the last named means generating an exciting impulse at the instant saidoutput waveform attains a preselected amplitude and means applying saidexciting impulse to said blanking impulse generating means.

2. The invention as set forth inclairn 1, said exciting means comprisinga square wave generator, means applying said output waveform to theinput of said square wave generator, said square wave generator beingresponsive to the instantaneous amplitude of said waveform to initiate asquare wave at a preselected value thereof and to the termination ofsaid waveform to terminate said square wave, means generating anexciting impulse coincident with the leading edge of said square waveand means applying said exciting impulse to said blanking impulsegenerating means.

3. A radio pulse echo system comprising a pair of directive antennas,each repetitively scanning a sector of space, a cathode-ray tube, meansgenerating a pair of voltages each varying in accordance with the scanof a respective one of said antennas, means generating on saidcathode-ray tube a discrete plan position indication of the output ofsaid system as derived from each of said antennas, said indicationgenerating means including means repetitively generating a saw-toothoutput voltage in synchronism with the pulse emission of said system,means responsive to said output voltage for repetitively deflecting theray of said cathode-ray tube in synchronism therewith, means applyingone of said pair of voltages tosaid sawtooth voltage generating means tovary the amplitude of said output voltage in accordance therewith, andmeans to clip portions of at least one of said indications which wouldotherwise overlap with portions of the other, said clipping meanscomprising means to generate blanking energy impulses and to apply saidblanking impulses to said cathode-ray tube in a manner to inhibit theexcitation of the screen of said tube for their duration, and meansresponsive to the amplitude of said saw-tooth output voltage to excitesaid blanking impulse generating means, said exciting means comprisingmeans having said saw-tooth output voltage applied thereto andgenerating an energy impulse at the instant the amplitude of saidsaw-tooth exceeds a predetermined value and means applying said energypulse to said blanking impulse generating means as exciting voltage.

References Cited in the file of this patent UNITED STATES PATENTS TaskerAug. 18, 1953

